The present invention relates to anti-ventilation plates, sometimes called anti-cavitation plates, in marine drives. The purpose of an anti-ventilation plate is to minimize the entrance of air to a submerged propeller therebelow.
The holding ability of a propeller is improved by maintaining the propeller submerged and by preventing the entrance of surface air to the propeller. Previous attempts to improve the holding ability of the propeller and to prevent the propeller from "breaking loose" have focused on propeller design, size of the anti-ventilation plate, or the gearcase shape below the water. It is desired to keep the aft end of the anti-ventilation plate in the water or at the surface when the boat is on plane and the engine is properly trimmed out. Prior attempts to achieve this relationship involved power trim systems or vertical adjustment mechanisms, but these significantly affect overall boat trim.
Boat acceleration is influenced by many factors, including boat design, propeller and engine trim position. If the propeller and engine trim position are optimum, and the boat still accelerates poorly, it is known in the art to provide trim tabs at the transom of the boat. The trim tabs act as a lever to help push the bow of the boat down resulting in a flatter running attitude, and increasing boat speed. The majority of engine installations dictate that the anti-ventilation plate be mounted about level with the boat bottom. For best acceleration, the engine is trimmed all the way in, i.e. under. In this position, the engine's thrust is working to push the transom of the boat up and the bow of the boat down. Once the boat starts to move, the anti-ventilation plate acts as a trim tab, or lever, helping to achieve the on-plane condition.
The present invention provides an improved anti-ventilation plate preventing the entrance of air to the propeller when the boat is on plane and trimmed out, and also providing improved acceleration performance.